Project Summary: This study will extend existing data and ongoing research to understand the dynamics of childhood obesity in a large population of children living in 400 communities that vary on environmental risk regulators. Using a comprehensive electronic health record from a large primary care health system, we will use multilevel and system dynamic models to study the dynamics of obesity in over 55,000 children. We will also conduct a nested substudy of 1150 children from a subset of 80 communities to examine how features of the environment, as well as diet and physical activity alter gene expression as captured by locus-specific DNA methylation in what will be the largest study of its kind to date. We will also employ systems-dynamic models, motivated by real data, to simulate the epidemiologic consequences of policy interventions to up- or down regulate system components identified as determinants of obesity from earlier models.